One of the issues that came up repeatedly during oral argument is that the EPA chose to regulate greenhouse gas emissions from stationary sources at a level much higher than the threshold set in the statute, and similarly, that the EPA expanded the PSD program—which originally covered certain air pollutants with area-specific impacts—to include greenhouse gases.  Immediately prior to this clip, Justice Alito asked Keisler, “Isn’t there a big difference [between greenhouse gases and other specific air pollutants] in that the quantity of greenhouse gases that are emitted by sources are much greater than the quantity of other pollutants . . .?”  Keisler agreed with Justice Alito, and added that because greenhouse gases do not have area-specific impacts on air quality they cannot be regulated by the PSD program under the Clean Air Act.   He argued that, therefore, the Clean Air Act’s limits on other pollutants should not apply to greenhouse gases.  After Keisler answers, Justice Breyer counters Keisler’s response—and Justice Alito’s question—by making an argument about bubble gum and the common practice of interpreting exceptions into statutes.